1. Field of the Invention
The present invention relates to an ignition time control device of an engine.
2. Description of the Related Art
To obtain good combustion at engine warmup when the engine temperature is low, it is necessary to advance the ignition timing compared with after warmup is completed. Therefore, in conventional engines, a reference ignition timing for warmup operation required for obtaining good combustion is found in advance by experiments and the ignition timing controlled to this reference ignition timing at the time of engine warmup.
On the other hand, in an internal combustion engine providing an exhaust gas purifying catalyst in the engine exhaust passage, it is necessary to have the exhaust gas purification action start as fast as possible after engine startup. Therefore, it is necessary to cause the temperature of the catalyst to rise as quickly as possible after engine startup. In an internal combustion engine, however, the temperature of the exhaust gas rises when the ignition timing is retarded. Accordingly, if the ignition timing is retarded from the reference ignition timing of engine warmup, it becomes possible to cause the temperature of the catalyst to rise early after engine startup.
In this case, however, if the ignition timing is retarded during engine high load operation, high engine output can no longer be obtained. That is, if the ignition timing is retarded during engine high load operation, high output can no longer be obtained when the vehicle driver desires a high output. Therefore, it is not desirable to retard the ignition timing during engine high load operation. Further, if the ignition timing is retarded during idling, the combustion becomes unstable. Therefore, it is not desirable to retard the ignition timing during engine idling.
Accordingly, there is known an internal combustion engine designed so as to control the ignition timing to a reference ignition timing during high load operation at the time of engine warmup or at the time of idling and so as to retard the ignition timing with respect to the reference ignition timing to promote the warming of the catalyst at the time of other operating states, that is, engine low load and medium load operation (see Japanese Unexamined Patent Publication (Kokai) No. 61-205377).
At the time of engine warmup in such an internal combustion engine, however, when deciding whether the operating state is a high load operating state where the ignition timing should be made the reference timing or the medium load operating state where the ignition timing should be retarded based on a representative value changing according to the atmospheric pressure and indicating the engine load, for example, the mass flow rate of the intake air or the absolute pressure in the intake passage downstream of the throttle valve, the problem arises that a high engine output cannot be obtained when driving a vehicle at a high altitude where the atmospheric pressure is low.
That is, in the case where, when the mass flow rate of the intake air is greater than a predetermined reference value at the time of engine warmup, for example, under the normal atmospheric pressure, it is judged that the operating state is one of a high load and the ignition timing is controlled to the reference ignition timing, even if the accelerator pedal is depressed hard when the vehicle is operating at a high altitude where the atmospheric pressure is low, the mass flow rate of the intake air will not reach the predetermined reference value and therefore it will be judged that the engine is operating at medium load. As a result, the ignition timing is retarded from the reference ignition timing and therefore a high output cannot be obtained even if the vehicle driver desires a high output.